So calendar sync appears back to normal on OC web interface, as well as android calendar. However when i turn the sync option on for tasks in DAVdroid, it appears that recurring events dissappear from Thunderbird. I have 5 calendars currently synced, and my calendar that has most of my entries was missing several or maybe all items that I have set to repeat every weekday. Any ideas, is this OpenTasks doing, or what? I understood that OpenTasks did not support recurring tasks, but it shouldn’t make them or events disappear unless they are modified from within OpenTasks. Point me to any relevant logs you may need and I’ll try to figure out how to get them. This has been pretty frustrating as I am using this calendar for work and personal. So the original issue of this post is fixed, should this be posted as another topic? Thanks.
SyncManager: failed sync operation ... SyncResult: syncAlreadyInProgress
When having an account with multiple address books and I hit the Sync All button, I get the following errors:
2020-11-10 23:38:02.736 1731-2188/? W/SyncManager: failed sync operation JobId=101047 ***/at.bitfire.davdroid.address_book u0 [com.android.contacts] USER ExpectedIn=0s EXPEDITED STANDBY-EXEMPTED(TOP) Reason=10197, SyncResult: syncAlreadyInProgress: true stats  2020-11-10 23:38:02.821 1731-2188/? W/SyncManager: failed sync operation JobId=109265 ***/at.bitfire.davdroid.address_book u0 [com.android.contacts] USER ExpectedIn=0s EXPEDITED STANDBY-EXEMPTED(TOP) Reason=10197, SyncResult: syncAlreadyInProgress: true stats 
In this specific case, it was an account with 3 address books.
It appears the sync was only successful for one of the three address books and failed for the other two, making the sync incomplete.
This is a real device running Android 10.0 and the problem is easily reproducible, so I can run further diagnostics.
Yes, please provide more information.